Partial acetylation of cotton fibers



PARTIAL ACETYLATION F COTTON FIBERS Esmond J. Keating, Albert S. Cooper,Jr., and Edmund M. Buras, In, New Orleans, La., assignors to the UnitedStates of America as represented by the Secretary of AgricultureApplication June 24, 1955, Serial No. 517,955

2 Claims. (Cl. 8-121) (Granted under Title 35, U. S. Code (1952), sec.266) A non-exclusive, irrevocable, royalty-free license in the inventionherein described, for all governmental purposes, throughout the world,with the power to grant sublicenses for such purposes, is hereby grantedto the Government of the United States of America.

This invention relates to the partial acetylation of cellulosic textilefibers, and provides an improved and more economical partial acetylationprocess.

Prior work resulted in the development of the practical process for thepartial acetylation of vegetable textile fibers described in AmericanDyestufi Reporter, March 29, 1954, pages 203208. By means of thatprocess, fibers such as cotton fibers are partially aceylated to adegree of substitution of from about 0.5 to 2, to improve their heat androt resistance and the like properties. In conducting the process, thefibers are activated by soaking them in an activating liquid consistingessentially of acetic acid containing enough acetic anhydride to convertto acetic acid the regain moisture present in the fibers. The activatedfibers are partially acetylated by reacting them with an acetylatingliquid consisting essentially of an acetylating mixture of aceticanhydride and acetic acid containing a catalytic amount of perchloricacid. The portion of the acetylating liquid which is not retained in theporous portions of the fibers can be recovered, reconstituted andre-used in the activation of a subsequent portion of fibers. And, in abatchwise operation, the excess acetylating liquid, i. e., the portionof the liquid which drains off from the fibers, or which is removed by aconventional mechanical extraction using squeeze rolls, centrifuges andthe like, can similarly be recovered and re-used a number of times.

However, as the partial acetylation process was heretofore conducted, inorder to utilize the acetic acid and acetic anhydride that did not reactin the partial acetylation reaction, it was necessary to fractionallydistill spent acetylating liquids consisting of either the recoveredacetylating liquids used in a batchwise operation that had been re-usedfor more than about 10 times, or the recovered acetylating liquids usedin a continuous operation.

A primary object of the present invention is to provide an improvedprocess for partially acetylating vegetable textile fibers by activatingthe fibers with acetic acid and partially acetylating the activatedfibers by a per chloric acid-catalyzed reaction with an acetylatingmixture of acetic anhydride and acetic acid; in which improved process,the unreacted acetic acid and acetic anhydride contained in spentacetylating liquids are utilized by chemically converting spentacetylating liquids to compositions suitable for reconstituting andreplenishing the activating liquid.

We have now discovered several rather unobvious facts about the partialacetylation process. The fibers can be activated in an aceticacid-acetic anhydride activating liquid that contains up to about 0.05%by weight of perchloric acid. The fibers which are soaked in such aperchloric acid-containing activating liquid entrain and ice remove someof the perchloric acid. Such perchloric acid-containing activatingliquids can be repeatedly replenished by the addition of mixtures ofacetic acid and acetic anhydride containing up to about 0.015%perchloric acid, without causing an undesirable increase in theperchloric acid concentration of the activating liquid. And, a spentacetylating liquid can readily be converted to a mixture of acetic acidand acetic anhydride suitable for replenishing the activating liquid bymixing the spent acetylating liquid with potassium acetate and isolatingthe resulting precipitate of potassium perchlorate.

In general, in accordance with the present invention, the process ofpartially acetylating vegetable textile fibers to a degree ofsubstitution of from about 0.5 to 2, by presoaking the fibers with anactivating liquid consisting essentially of acetic acid containingenough acetic anhydride to convert to acetic acid the regain moisturepresent in the fibers and partially acetylating the activated fibers byreacting them with an acetylating liquid con sisting essentially of anacetylating mixture of acetic anhydride and acetic acid containing acatalytic amount of perchloric acid, is improved by: mixing anacetylating liquid, which was recovered from the partial acetylation ofa preceding portion of fibers and which is unsuited for reconstitutionand re-use as an acetylating liquid, with enough potassium acetate toneutralize from about to 100% of the amount of perchloric acid containedin the acetylating liquid; mechanically removing the resultingprecipitate of potassium perchlorate; and using the remaining liquid,along with enough of at least one liquid of the group consisting ofacetic acid and acetic anhydride to reduce the proportion of perchloricacid in the liquids used to not more than 0.015% by weight, toreconstitute and replenish the activating liquid.

The potassium acetate which is mixed with the spent acetylating liquidis preferably employed in the form of a solution of potassium acetate inacetic acid or water. The liquid that remains after the spentacetylating liquid has been freed of potassium perchlorate can either bemixed with enough acetic acid or acetic anhydride to produce a solutionin which the proportion of perchloric acid is less than about 0.015%prior to using it to replenish the activating liquid, or can be mixedwith the activating liquid before, during, or after such an amount ofacetic acid or acetic anhydride is mixed with the activating liquid.Where these liquids are separately mixed, both the acetylating liquidfrom which most of the perchloric acid has been removed and the aceticacid or acetic anhydride should be mixed with the activating liquidbefore the activating liquid is used to activate fibers.

In the accompanying drawing, Fig. l and Fig. 2 are flow sheetsillustrating a batchwise and continuous process, respectively, ofpartially acetylating cotton cloth and cotton yarn, respectively.

The following examples are illustrative of the details of at least onemethod of practicing the invention.

Example 1 A batch of purified cotton cloth amounting to 100 parts ofcotton and 6 parts of regain moisture was sub jected to the batchwiseprocess of partially acetylating vegetable textile fibers shown inFigure 1, using an acetylating liquid which had been used to acetylateprevious batches of fibers. The partially acetylated cloth was freed ofexcess liquid by means of squeeze rolls.

The recovered liquid was a spent acetylating liquid consisting of 161parts acetic acid, 13.2 parts acetic anhydride and 0.3 part perchloricacid. An amount of potassium acetate, 0.279 part, equivalent to about ofthe perchloric acid contained in the acetylating liquid, was dissolvedin 2 parts of acetic acid and mixed with, the spent acetylating liquid.

The mixed liquids were allowed to stand overnight, to insure thesettling of the resulting precipitated potassium perchlorate, and thesupernatant liquid was mechanically isolated by decantation. Thepotassium perchlorate-free liquid consisted of about 7.6% aceticanhydride, 92.3 acetic acid and 0.01% perchloric acid.

The potassium perchlorate-free liquid was added to the activating liquidstorage tank along with an additional 20.8 parts of acetic anhydride.The so-supplemented activating liquid was used as the activating liquidin the partial acetylatic-n of another 100 part batch of the same clothby the same procedure. Its use resulted in a normal reaction thatproduced a normal partially acetylated cloth.

it will be noted on the flow sheet that the potassium perchlorate-freeliquid contained the required amount of acetic acid, 160 parts, plusapproximately /3 of the required amount of acetic anhydride, 13.2 parts,needed for replenishing the presoal; bath.

A comparison of the cost of this process of utilizing the unconvertedreactants present in the excess reactant liquid, with the cost of thefractional distillation and purification steps heretofore practiced,indicated that the overall cost of the batch process for the partialacetyla tion of cotton fabric was materially reduced by use of thisimproved reclamation process.

Example 2 A lot of 8/5, purified cotton yarn amounting to 121.9 parts ofcotton and 9.1 parts of regain moisture was subjected to the continuousprocess of partially acetylating vegetable textile fibers as shown inFigure 2. The partially acetylated yarn was freed of excess liquid bymeans of squeeze rolls.

The recovered liquid was a spent acetylating liquid amounting to 306.3parts and consisting of 182.8 parts acetic acid, 121.9 parts aceticanhydride and 1.6 parts of perchloric acid. An amount of potassiumacetate, 1.6 parts, equivalent to all but 0.007% of the perchloric acidconcentration, was dissolved in 7.6 parts of water and mixed with thespent acetylating liquid.

The mixed liquids were allowed to stand overnight, to insure thesettling of the resulting precipitated potassium perchlorate, and thesupernatant liquid was mechanically isolated by decantation. Thepotassium perchlorate-free liquid consisted of about 26.1% aceticanhydride, 73.89% acetic acid and 007% perchloric acid.

The potassium perchlorate-free liquid was pumped to the activation feedtank and used as feed solution for the activation bath in the continuouspartial acetylation of another 121.9 part lot of the same yarn by thesame procedure. Its use resulted in a normal reaction that produced anormal partially acetylated yarn.

A comparison of the cost of this process with the cost of the fractionaldistillation and purification steps heretofore practiced, indicated thatthe overall cost of the continuous process for the partial acetylationof cotton yarn was materially reduced by use of this improvedreclamation process.

We claim:

1. In a process of partially acetylating cellulosic textile fibers to adegree of substitution of from about 0.5 to 2 by, presoaking the fibersin an activating liquid consisting essentially of acetic acid containingan amount of acetic anhydride sutficient to convert to acetic acid theregain moisture present in the textiie material, then acetyiating theactivated fibers by reacting them with an acetylating mixture of aceticanhydride and acetic acid containing a cataiytic ant-cunt of perchloricacid, the steps comprising mixing an acetylating liquid, which wasrecovered from the partial acctylaticn of a preceding portion of fibersand which is unsuited for reconstitution re-use as an acetylatingliquid, with enough potassium acetate to nontralizze from about to ofthe perchloric acid contained in the acctylating liquid, mechanicallyremoving the resulting precip e of potassium perchlorate mixing theremaining liquid with enough of at least one liquid of the groupconsisting of acetic acid and acetic anhydride to form a liquidcomposition in which the proportion of perchloric acid is not more thanabout 0.015% by weight, and mixing said liquid composition with saidactivating liquid to produce a reconstituted and replenished activat ingliquid containing up to about 0.05% by weight oi perchloric acid.

2. A process comprising mixing a spent acetylating liquid unsuited forreconstitution and reuse as an acetylating liquid for cellulosic textilefibers and consisting essentially of acetic acid, acetic anhydride, andan amount of perchloric acid exceeding about 0.05% by weight of saidliquid with enough potassium acetate to neutralize from about 85% to100% of the perchloric acid, removing the resulting precipitate ofpotassium perchlorate, mixing the resulting liquid with a sufiicientamount of at least one liquid of the group consisting of acetic acid andacetic anhydride to reduce the proportion of perchloric acid in theresulting mixture to a value not exceeding 0.0l5% by Weight, therebyproducing a liquid composition suitable for reconstituting andreplenishing the activating liquid used to activate cellulosic textilefibers prior to their partial acetylation to a degree of substitution offrom about 0.5 to 2, and mixing said liquid composition with saidactivating liquid, to produce a reconstituted and replenished activatingliquid containing up to about 0.05% by weight of: perchloric acid whichis suitable for activating cellulosic textile fibers prior to theirpartial acetylation to a degree of substitution of from about 0.5 to 2.

Buras et al.: Practical Partial Acetylation of Cotton, American DyestutfReporter, March 29, 1954, pages 203 208 (page 206, last paragraph reliedon).

1.IN A PROCESS OF PARTIALLY ACETYLATING CELULOSIC TEXTILE FIBERS TO ADEGREE OF SUBSTITUTION OF FROM ABOUT 0.5 TO 2 BY PRESOAKING THE FIBERSIN AN ACTIVATING LIQUID CONSISTING ESSENTIALLY OF ACETIC ACID CONTAININGAN AMOUNT OF ACETIC ANHYDRIDE SUFFCIENT TO CONVERT TO ACETIC ACID THEREGAIN MOISTURE PRESENT IN THE TEXTILE MATERIAL, THEN ACETYLATING THEACTIVATED FIBERS BY REACTING THEM WITH AN ACETYLATING MIXTURE OF ACETICANHYDRIDE AND ACETIC ACID CONTAINING A CATALYTIC AMOUNT OF PERCHLORICACID,THE STEPS COMPRISING MIXING AN ACETYLATING LIQUID, WHICH WASRECOVERED FROM THE PARTIAL ACETYLATION OF A PRECEDING PORTION OF FIBERSAND WHICH IS UNSUITED FOR RECONSTITION AND RE-USE AS AN ACETYLATINGLIQUID,WITH ENOUGH POTASSIUM ACETATE TO NEUTRALIZED FROM ABOUT 85 T 100%OF THE PERCHLORIC ACID CONTAINED IN THE ACETYLATING LIQUID, MECHANICALLYREMOVING THE RESULTING PRECIPITATE OF POTASSIUM PERCHLORATE MIXING THEREMAINING LIQUID WITH ENOUGH OFAT LEAST ONE LIQUID OF THE GROUPCONSISTING OF ACETIC ACID AND ACETIC ANHYDRIDE TO TO FROM A LIQUIDCOMPOSITION IN WHICH THE PROPORTION OF PER CHLORIC ACID IS NOT MORE THANABOUT0.015% BY WEIGHT AND MIXING SAID LIQUID COMPOSITION WITH SAIDACTIVATING LIQUID TO PRODUCE A RECONSTITUTED AND REPLENISHED ACTIVATINGLIQUID CONTAINING UP TO ABOUT 0.05% BY WEIGHT OF PERCHLORIC ACID.